Radioactive Iodine in the Treatment of Type-2 Amiodarone-Induced Thyrotoxicosis

Abstract

Amiodarone-induced thyrotoxicosis (AIT) is usually classified into two types: type 1, in which a high iodine content triggers the autonomous production of thyroid hormone; and type 2, in which destructive thyroiditis causes the release of preformed thyroid hormone. AIT is a difficult management problem that sometimes requires ablative thyroid therapy. The use of radioactive iodine (RAI) therapy in patients with type-1 AIT who had a 24-hour radioactive iodine uptake (RAIU) value of >10% has been previously reported. Despite its documented efficacy at usual doses (10-30 mCi) in patients with type-1 AIT, the efficacy of RAI in those with type-2 AIT has never been questioned, because type-2 patients usually have low RAIU. We thought that high adjusted-dose RAI might be an attractive alternative to thyroid gland ablation in patients with type-2 AIT. Four patients with type-2 AIT who required thyroid ablation were included in the study. These individuals were either poor candidates for surgery or had refused surgery. The size of the thyroid gland in all subjects was within normal limits, and each thyroid was characterized by a homogenous echotexture on ultrasonography, the absence of vascularity on Doppler sonography, a low (<4%) 24-hour RAIU value and the absence of thyroid autoantibodies-all of which are characteristic of type-2 AIT. The patients were initially treated with thionamides and glucocorticoids. All patients except one achieved euthyroidism before RAI therapy. All four patients received one dose of RAI (range 29-80 mCi) and followed up for 12 months. No exacerbation of thyrotoxicosis was noted after RAI therapy. Hypothyroidism (in three patients) or euthyroidism (in one patient) was achieved in first six months. In patients with type-2 AIT, RAI treatment may be the therapy of choice for thyroid gland ablation.